Radiation-sensitive compositions are routinely used in the preparation of imageable materials including lithographic printing plate precursors. Such compositions generally include a radiation absorbing compound or sensitizer, a binder, and in some instances initiator compositions and polymerizable components, each of which has been the focus of research to provide various improvements in physical properties, imaging performance, and image characteristics.
Recent developments in the field of printing plate precursors concern the use of radiation-sensitive compositions that can be imaged by means of lasers or laser diodes. Laser exposure does not require conventional silver halide graphic arts films as intermediate information carriers (or “masks”) since the lasers can be controlled directly by computers. High-performance lasers or laser-diodes that are used in commercially-available image-setters generally emit radiation in a specific region of the electromagnetic spectrum, and thus the radiation-sensitive compositions are required to be sensitive in the regions appropriate for a specific imaging laser.
Radiation-sensitive compositions and the imageable elements in which they incorporated are generally either negative-working or positive-working. For negative-working imageable elements, exposed regions in the radiation-sensitive compositions are hardened and non-exposed regions are usually washed off during development. For positive-working imageable elements, the exposed regions are dissolved in a developer and the non-exposed regions become an image.
The literature that describes various components of such imageable elements includes hundreds of publications, and thus they are too numerous to mention here. The patent literature is full of teaching relating to various problems that the industry has been addressing for the last several decades, especially as the “computer-to-plate” (CTP) imageable elements and equipment became prominent in the 1990's. Thus, there has been considerable efforts to develop both positive- and negative-working elements with high imaging sensitivity (high photospeed), fast developability in various developing solutions (generally alkaline in pH), high resistance to degradation to pressroom chemicals (“chemical resistance”), plate durability, storage stability, high image stability, low environmental impact, and high run length.
Some of these problems have been solved by designing unique polymeric binders that are used in imageable layers to provide a matrix for the various imaging components. For example, U.S. Pat. No. 4,511,645 (Kioke et al.) describes the use of polymeric binders having unsaturated side chains in negative-working imageable elements to stabilize image formation. In addition, EP 0 924 570A1 (Fujimaki et al.) describes UV/visible-sensitive compositions and imageable elements containing polymeric binders having amido groups in side chains to increase alkaline solution solubility.
WO 2004/074930 (Baumann et al.) describes the use of polymeric binders having carboxylic acid side groups in combination with oxazole derivatives in UV-sensitive negative-working imageable elements. Such polymeric binders are also used with benzoxazole derivatives in UV-sensitive negative-working imageable elements, as described for example, in WO 2007/090550 (Strehmel et al.).
WO 2004/035687 (Loccufier et al.) describes the use of phenolic polymeric binders in positive- or negative-working imageable elements, which polymeric binders include a thio-linked heterocyclic group attached to the phenolic recurring units in order to increase the chemical resistance of the imageable layers. The heterocyclic groups can be any of a wide variety of sulfur, oxygen, or nitrogen-containing heterocyclic groups.